Survey of Asian and Pacific species of Hedyotis and Exallage (Rubiaceae) with nomenclatural notes on Hedyotis types

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Abstract:

Selection of a type species for the wide-ranging genus Hedyotis (Hedyotideae; Rubiaceae) has involved a long-standing controversy over two species, Hedyotis auricularia L. and H. fruticosa L. Nomenclatural and morphological data support the selection of H. fruticosa as type. The choice of H. auricularia would have caused considerable taxonomic confusion by upsetting previously established names and overturning the names of the many species of Oldenlandia. The General Committee on nomenclature recently has approved Hedyotis fruticosa as the conserved type of Hedyotis. The morphology and taxonomy of the genus Exallage, based on H. auricularia, is surveyed, and we conclude that at least three of the species are better treated as a new subgenus of Oldenlandia. The synonymy of these species is listed, and two new combinations are published in the genus Oldenlandia. A detailed survey of the species related to Hedyotis fruticosa begins with the 24 Sri Lankan species, most of which exhibit morphological characters similar to Hedyotis fruticosa. The capsules of these species have been termed diplophragmous in allusion to the partial apical loculicidal dehiscence followed by complete septicidal dehiscence, resulting in two separate capsular halves or cocci. The seeds of these species are dorsiventrally compressed with a ventral hilar ridge topped by a punctiform apical hilum. Many other Asian and Pacific, particularly Micronesian, species show similar diplophragmous capsules and fruticosa-type seeds. The recognition of this newly circumscribed group, Hedyotis subgenus Hedyotis, ranging from China and India to Micronesia, establishes a firm basis for comparative studies of Hawaiian and American species, which are known to differ in morphology from the typical subgenus.

Keywords: ASIA; EXALLAGE; HEDYOTIS; MORPHOLOGY; OLDENLANDIA; PACIFIC; RUBIACEAE; TAXONOMY; TYPIFICATION

Document Type: Research Article

Affiliations: Department of Systematic Biology - Botany, National Museum of Natural History, MRC-166, Smithsonian Institution, P.O. Box 37012, Washington, D.C. 20013, U.S.A.

Publication date: November 1, 2003

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